Send Orders of Reprints at reprints@benthamscience.org Current Pharmaceutical Design, 2013, 19, 11-16 11 Role of Nitric Oxide in the Central Interferon-alpha-induced Inhibition of Gastric Acid Secretion in Rats József Czimmer 1,* , Ágnes Király 1 , Imre László Szabó 1 , Gyula Mózsik 1 and Gábor Süt 2 1 First Department of Medicine, Medical School, University of Pécs, Hungary; 2 Department of Immunology and Rheumatology, Medi- cal School, University of Pécs, Hungary Abstract: Cytokines are known to play a key role in regulation of gastric functions. Interferon-alpha (IFN-) has been published to im- pair gastric motility. Aims of this study were to clarify effect of IFN- on gastric acid secretion (GAS) and determine role of nitric oxide (NO) in the process. Both subcutaneous (1000, 10000, 100 000 IU, s.c.) and intracisternal (10, 100, 1000 IU, i.c.) injections of IFN- dose-dependently inhibited GAS induced by pylorus ligation in male SD rats in 2 hrs (370±40, 233±39, 208±50 micromol vs control 415±59 micromol and 481±50, 249±75, 141±25 micromol vs control 485±65 micromol, respectively). Central doses inducing same level inhibition were 100 times lower. NOS inhibitor L-NAME (3 mg/kg, i.v.) blocked the inhibitory effect of i.c. ED50 dose 100 IU IFN- (507±75 micromol/2 hrs), while L-arginine, the substrate of nitric oxide synthase (NOS) prevented L-NAME action (266±82 micromol/2 hrs). D-arginine failed to prevent L-NAME action on IFN--induced inhibition of GAS. Aminoguanidine, a selective inhibitor of induc- ible NOS (iNOS) failed to block IFN- induced inhibition of GAS. Results suggest that IFN- inhibits GAS centrally through nitric oxide pathways probably mediated by continuous isoform of NOS that can be important in regulation of GAS in healthy or pathological conditions. Keywords: Brain-gut interactions, cytokines, NOS inhibitors, iNOS, cNOS, peripheral and central interferon-alpha action, vago-vagal reflex, central nervous system, pylorus ligation. INTRODUCTION Different gastrointestinal functions are regulated by well- documented interactions among central nervous system (CNS), immune and endocrine systems [1]. It has been established that neuropeptides and cytokines have important role in the regulation of gastric functions in rodents, including gastric acid secretion as well [2-8]. Interferons (IFN’s), a 165-172 amino acid cytokine family have key role in immune response to viral and parasitic infections and certain tumors [9,10]. There are two main groups of interferons: type I interferons (IFN-, IFN-, IFN-, IFN-, IFN-, IFN-, IFN- ) and type II interferon (IFN-) [11]. Human IFN- was cloned in 1980, and was found to represent a mixture of several closely re- lated proteins expressed from distinct genes [12]. The production of IFN- by virally infected cells induces resistance to viral replica- tion, enhances MHC class I expression, increases antigen presenta- tion, and activates natural killer cells to kill virus-infected cells [13- 16]. Members of the IFN`s family can be detected in almost all types of tissues, i.e. in brain tissues, even in the absence of a spe- cific inducer. Several biological stimuli, such as viral, bacterial, mycoplasma or protozoa infections, exposure to certain cytokines and growth factors such as interleukin-1, interleukin-2 or tumor necrosis factor- highly increase IFN- biosynthesis in CNS [17]. It has been shown that treatment with IFN- inhibited gastric emp- tying of isotope labelled solid food in humans suffering from hepa- titis C virus infection [18]. IFN--induced inhibition of gastric emptying which can be reversed by cisapride, a cholinergic and serotoninergic agonist in humans [18]. However there is little known regarding the effect of IFN- on gastric secretion. IFN- injecton into the central nervous system results in fever [19], hypal- gesia, anorexia and loss of weight [20]. Some CNS effects of IFN- are mediated by changes of neuronal activities [21]. IFN- de- creases the activity of medial preoptic area neurons through the activation of opioid receptors and consequent activation of CRF *Address correspondence to this author at the Department of Gastroenterol- ogy, Medical School, University of Pécs, Rákóczi u. 2., Pécs, Hungary, H-7623; Tel: + 36 72 536 000; E-mail: jozsef.czimmer@aok.pte.hu neurons resulting in the peripheral inhibition of NK cell cytotxicyty through sympathetic nervous system [21]. One of the modulators influencing IFN- MPO neuron interaction is nitric oxide [21-23]. Nitric oxide (NO), a free radical is known to be a key mediator of the regulation of both gastric motility and secretion [24-26]. NO is produced by nitric oxide enzyme (NOS). Enzyme NOS has con- stitutive (eNOS, nNOS) and inducible isoforms (iNOS) depending whether their NO production is continuous or can be induced by a stimulus [24, 27-28]. NG-nitro-L-arginine methyl ester (L-NAME) is a specific and non-selective competitive antagonist of the NOS isoenzymes [29]. Inducible isoform of NOS can be selectively inhibited by amino- guanidine [30-31]. The aim of observations was to investigate the effect of IFN- on gastric secretory function using a pylorus ligation rat model. The site of action was studied whether it is peripheral or regulated by the central nervous system. Pylorus ligation has been shown to induce a potent increase of gastric acid secretion via a vago-vagal reflex and adrenoceptor stimulation in rats [32]. We further aimed to find out whether nitric oxide has a role in IFN- action on gastric secretion and to clarify whether the continuous or the inducible isoform of NOS is involved. Male CFY rats weighting 180-220 g were maintained under controlled housing conditions (temperature 21,5- 23,5 °C). Food (Standard Purina rat chow) and water were available ad libitum. Rats were deprived of food for 18 hours before the experiments, but had free access to water up to the time when gastric acid secretion was measured. All experiments were performed between 10 a.m. and 14 p.m. Animals were anesthetized with inhalation of diethyl-ether (BP 88/USP 22, Roche-Lez-Beaupré) for 10 minutes, meanwhile pylo- rus was approached through median laparotomy, then ligated with width (3 metric) surgical thread. Finally the abdomen was closed by suture and the skin was clumped (14 mm clumps, AGRAFES DE MICHEL). Rats were euthanized by inhalation of carbon dioxide two hours later. Stomachs were clamped at the pylorus and cardia, then removed and their contents were collected. Samples were cen- 1873-4286/13 $58.00+.00 © 2013 Bentham Science Publishers